Diethanol sulfone-formaldehyde modification of cellulose catalyzed by a lewis acid salt



United States Patent DIETHANOL SULFONE-FORMALDEHYDE MODI- FICATION (3F CELLULOSE CATALYZED BY A LEWIS ACID SALT Kurt H. Tauss, Mobile, Ala, assignor to Courtaulds North America Inc, New York, N.Y., a corporation of Alabama No Drawing. Filed Mar. 25, 1%3, Ser. No. 267,834

19 Claims. (Cl. 8-1164) This invention relates to a process for improving the properties of cellulose, in particular cellulose textile material, to solutions for use in such process and to the improved cellulose products resulting therefrom.

At the present time there is a very substantial demand for processes which are capable of imparting wash-Wear properties to cellulosic textile materials. Wash-wear properties are those which make it possible for a fabric to assume a smooth freshly pressed appearance after washing and drying without having been actually pressed.

Among the reagents which are currently used to impart wash-wear properties to cellulosic textiles is diethanolsulfone, HO--CH CH -SO CH CH OH. This substance is conventionally applied to cellulosic fabrics in the presence of alkali. Under these conditions, the agent loses water to form divinyl sulfone:

Divinylsulfone reacts with cellulose by vinyl addition, cross-linking the cellulose:

Cellulose cross-linked in this manner has improved properties in various respects and in particular the wet crease recovery angle 1 is very substantially improved.

1 Crease recovery angle is defined in 1958 Technical Manual AATCC p. 157.

While the method as described has had a certain degree of commercial success, it has certain drawbacks, viz:

(l) The fabric as treated acquires a distinct yellow color. This requires peroxide bleaching, which is expensive.

(2) Proper stabilization of goods requires about 8% diethanol sulfone on cotton and about 16% on rayon. This makes the treatment prohibitively expensive for many fabrics.

(3) The treated fabric is very sensitive to strong alkali. Boiling in an alkali solution hydrolyzes the sulfone-cellulose bonds.

(4) The light fastness of many dyed fabrics is severely and adversely affected.

It has now been discovered that diethanol sulfone can be bonded to cellulose by means of formaldehyde, using as a catalyst or cu-ring agent a metallic salt which is a Lewis acid in the solid state. The novel process apparently operates by the following mechanism:

In any case, it is clear that the mechanism involved is quite different, and gives a different product from the mechanism and product of conventional diethanol sulfone treatments. While conventional treatments require'alka- 'ice line catalysts, at pH 10 or above, the present treatment is substantially independent of pH and can be carried out under neutral or acid conditions, as will best suit the fabric being treated. Products of the present process are highly resistant to alkaline hydrolysis. Moreover, although the formation of divinylsulfone is apparently a necessary intermediate step for reaction of diethanol sulfone under conventional alkaline catalysts, divinyl sulfone as such cannot be reacted with cellulose under the present system.

The invention thus comprises, in its process aspects, 2. new method for improving the properties of cellulose which comprises impregnating cellulose with diethanol sulfone, with formaldehyde and with a metallic salt which is a Lewis acid in the solid state, and curing the impregnated cellulose.

In another aspect the invention includes an aqueous solution suitable for treating cellulose which comprises diethanol sulfone, formaldehyde and a metallic salt which is a Lewis acid in the solid state.

In still another aspect the invention comprises cellulose cross-linked by a reaction product of formaldehyde and diethanol sulfone.

The novel process can be applied to various cellulose materials but is particularly advantageous when used with cellulose textile materials. Cellulose textile materials to which the invention is applicable may be of natural origin such as cotton, linen, hemp, jute, ramie or sisal, or of synthetic origin, i.e. rayon, made by the viscose, cuprammonium or nitrate process or by the saponification of organic esters of cellulose, e.g. cellulose acetate.

The textile material may be treated in the form of staple fiber, as continuous filament, in the form of tow, yarn or thread. The process can also be applied to structures containing cellulose fibers. The structure may be Woven or knitted textile fabrics, or textile fabrics of other kinds, for example, the so-called non-woven fabrics, or even paper.

The formaldehyde used may be added to the treating solution as the normal 40% aqueous commercial solution. Other sources, e.g. paraformaldehyde, may, however, be used as desired.

As noted above, the present process requires .a metallic salt which is a Lewis acid in the solid state.

In determining whether any given salt is a Lewis acid, the procedure described by Walling, JACS, 72, pp. 1164- 1168, and Pines and Haag, JACS 82, pp. 2471-2483, may be used. A particularly suitable test is to take a small quantity of the salt, dried to remove surface moisture, and allow it to stand overnight with a solution of the leuco base of Malachite Green (4,4-di(dimethylamino)- triphenyl methane) in a dry, non-polar solvent such as cyclohexane or isooctane. The development of a green color at the salt surface indicates that the salt is a Lewis acid. An alternative test may be based on the response of a compound to an indicator such as Methyl Red (whose range in aqueous solution is pH 4.46.2) under the conditions described by Walling (72, JACS,1164). Indicators such as Methyl Red have the drawback of giving positive reactions in the presence of traces of acid (in the classical sense). On the other hand, the Malachite Green leuco base reaction appears to be inhibited by traces of classical acids.

In addition to being a Lewis acid, the curing agent should be soluble and form no precipitate in water at the operating pH, at concentrations of at least 0.03 mol/ liter. Salts which remain soluble at pH up to say 10 are, of course, more advantageous. Obviously, salts which are highly colored or highly toxic or become so during the process are undesirable, though not necessarily inoperable in the process.

Salts which meet these qualifications are in general to be found among those in which the metal is bivalent and belongs to Group II of the Periodic Table and the acid radical is that of a strong monobasic acid which is at least 50% ionized in normal aqueous solution at 18 C., such as hydrochloric, hydrobromic, hydriodic, nitric, perchloric and thiocyanic acids. Of most interest are salts of calcium, magnesium, strontium and barium.

Examples of suitable salts would include CaCI CaBr m a)2, )2 3)2 a, g a Mg(ClO and MgI as well as SrCl and BaCl Either the anhydrous salt or a hydrate may be used, as may mixtures of salts. Generally the magnesium salts are preferred. The magnesium halides are especially favored and of these magnesium chloride is outstanding.

The diethanol sulfone used in the present invention may be obtained from any suitable source. The commercially available 40% aqueous solution sold by General Aniline and Film Corp. as Ganalok A-14 is satisfactory.

In practicing the novel process, all three principal ingredients, i.e. the diethanol sulfone, the formaldehyde and the Lewis acid can and preferably are applied frorh the same aqueous solution. In the preferred form of the invention, the cellulose, after impregnation in said aqueous solution to a controlled Wet pickup, is heated to remove Water and then cured to establish co-valent bonding. Separate solutions of Lewis acid, diethanol sulfone and formaldehyde can, of course, be employed, but there is no advantage in so doing. In any case, all three ingredients are deposited on the cellulose before curing.

The concentration of formaldehyde in the solution from which it is applied may vary to a considerable extent, depending on whether natural or regenerated cellulose is treated, on the physical form of the fiber and on the effect which it is desired to secure by means of the formaldehyde.

An overall range of recommended concentrations would extend from about 0.5% to about by weight. Rayon fabric will normally require 1% to 10%; cotton fabric 0.5% to 5%, by weight, It will be understood that higher concentrations may be employed, but severe no useful purpose.

The concentration of curing agent may vary considerably, depending on the agent. Normally it will be between about 0.03 and about 0.9 mol/liter; preferably between about 0.1 and about 0.45 mol/liter. However, in any case, the amount of curing agent deposited on the cellulose should be at least 0.003 mol/1.00 g. of cellulose; normally between about 0.0038 and about 0.09, preferably between about 0.008 and about 0.054 mol per 100 g. of cellulose.

The pH of the solution or solutions may vary widely; in fact it is one of the advantages of the present process that it is substantially independent of pH. It is significant that while conventional processes employing formaldehyde in cross-linking invariably require low pH and conventional processes using diethanolsulfone require high pH, the present process using both formaldehyde and diethanolsulfone can be run at either low or high pH, and the pH which is used in any particular case may be determined by other considerations. In this connection it may be pointed out that the physical properties, e.g. tensile strength, of cellulosic material is adversely affected by acid solutions. For this reason it is normally desirable to use neutral or nearly neutral solutions. Alkaline solutions may be used at pHs up to those at which the Lewis acid will be precipitated. In general, the process can be carried out from say pH 1 (or even lower, depending on the degree of cellulose degradation that can be tolerated) to pH 10. It is preferred to operate at say pH 5 to pH 9, especially at pH 6 to pH 8.

The concentration of diethanol sulfone used in the treating solution may vary to a considerable extent depending on the fabric treated, the effect desired and the quantity of formaldehyde to be applied. Generally the concentrations required will be considerably less than are required in the conventional case of alkaline fixation and in general solutions containing at least 1% and up to say 10% will be used. It should be understood, however, that the amount of diethanol sulfone deposited on the cellulose is more significant than the concentrations in solution; and in general it is found that at least 1 and not more than say 6% of diethanol sulfone (based on bone dry cellulose) should be applied to the cellulose. It will be understood that these limits are not critical. However, if less than about 0.5 of diethanol sulfone is fixed to the cellulose, the benefits of the process will not be obtained; conversely, if more than 6% is applied, the excess is of no particular benefit.

The temperature of the solution is of no'special significance, though high temperatures are generally avoided to suppress volatilization of formaldehyde. Conveniently thce solution is used at room temperature, say 15 to 30 The treating solution can be applied to the cellulose in any convenient manner. Normally, in the case of fabric, the material is padded through the solution. Other conventional methods such as spraying, may however. be used as desired.

Following application of the treating solution, the impregnated material is dried and cured.

The conditions under which the curing is effected will depend on the nature of the curing agent. Usually the material will first be dried at say 60-ll0 C. for whatever time (normally not more than about 30' minutes) is required to reduce the moisture content to say 5% by weight of the bone dry material. Curing is then conducted by heating to temperatures from about C. to about 190 C. for periods which may range from say 30 minutes to a few, say about 5, seconds. Where the pH is high, more rigorous curing conditions will be required than when a neutral solution is employed.

By their nature most Lewis acids are capable of forming hydrates and since the present treatment involves application of aqueous solutions, the curing agent is normally deposited as a hydrate. With most salts at least a part of the hydrate water is evolved during curing. It has been found that during this water evolution the cellulose-formaldehyde reaction is inhibited or at least markedly depressed. To avoid such inhibition or depression it is therefore desirable to conduct the curing at temperatures either above, below or between the range or ranges at which the particular curing agent used loses large amounts of water of hydration.

Since it is desirable to conduct curing as expeditiously as possible temperatures below dehydration temperature are not usually employed. At the same time extremely high temperatures are to be avoided for fear of damage to the cellulose.

Because of these factors, salts which are Lewis acids and which can be heated at intermediate temperatures without water evolution are extremely desirable as curing agents, other things being equal. One of the properties that makes magnesium chloride especially attractive as a curing agent in the present process is that although it loses some water at about 0., there is an intermediate temperature range in which comparatively little water is evolved and the compound can therefore functron effectively as a curing agent without a prolonged curing time or an excessively high temperature.

Obviously the drying and curing steps may be combined in a single treatment, if desired.

As is customary in conventional procedures using alkaline catalysis, the cellulose may be subjected to a hot soap wash to remove unfixed diethanol sulfone.

During curing, the formaldehyde and the diethanol sulfone become bound to the cellulose. The product obtained contains between about 0.1% and about 7% formaldehyde and between about 0.5 and about 5% diethanol sulfone, chemically bound to the cellulose. As noted above, the formaldehyde is considered to be present in the form of polyoxymethylene groups linking diethanol sulfone groups to cellulose or to one another.

Cellulose treated according to the invention shows properties typical of cross-linked cellulose. Its water imbibition is greatly reduced compared with untreated material. For example, the water imbibition of conventional textile grade regenerated cellulose staple fiber is about 100-115% whereas the water imbibition of the present product can be reduced to say 30-40%. Similarly, regenerated cellulose treated in accordance with the invention shows much greater resistance to swelling in caustic soda and can be mercerized without difficulty. It is insoluble in cuprammonium hydroxide.

Cellulose fabrics treated in accordance with the invention show greatly improved crease recovery properties both wet and dry. For example, in most cases the crease recovery, wet and dry, of fabrics treated according to the invention is increased by at least 50 (W-l-F) and in some cases it may be increased by as much as 150 (W-l-F). This is unusual, since processes which impart dry crease recovery do not usually also impart an equal level of wet crease recovery, and vice versa.

The invention will be further described with reference to the following specific examples which are given for purposes of illustration only and are not to be taken as in any way limiting the invention beyond the scope of the appended claims.

Example 1 This example illustrates a technique which may be used to determine whether or not a given salt is a Lewis acid capable of cross-linking cellulose.

The leuco base of Malachite Green is purified by repeated recrystallization from absolute methanol until the solid gives no green color when dissolved in glacial acetic acid. A 0.5% by weight solution of the purified base in pure cyclo-hexane is then prepared.

Approximately 510 g. of the salt to be tested is spread on a shallow dish and placed in a moving air stream at 80 C. for about 30 minutes. A small portion, say 0.5 g. of the dried salt is then placed in a test tube and 2 to 3 ml. of the leuco base-cyclohexane solution is added to the tube.

The mixture is allowed to stand for 12 hours. The development of a green color on the surface of the salt at the salt-liquid interface indicates that the salt is a Lewis acid.

The results obtained with this test on a few salts are listed in Table I below. In the table positive means that a green color developed.

TABLE I Salt: Reaction MgCl POSlllVB. A12(SO4)3 DO. Zn(NO Do. CuSO Do. CaCl Do. (NH 80 Negative. (NH HPO magnesium acetate Do. [Mg(C H O -4H O] Do.

Similar results can be obtained using a 0.1% solution of Methyl Red in isooctane in place of the Malachite Green leuco base solution.

Care should be taken to see that prior to testing the salts are dried to remove surface water, since this will interfere with the above tests. For example, if CaCl or MgSO -7H O are permitted to stand in the air for several hours and tested without drying, they will give no color. Yet if properly dried, as outlined above, they will give a positive test and, with proper curing temperatures, can be made to promote the formaldehyde-cellulose reaction.

Example 2 Samples of never-dried viscose rayon staple fiber 1 /2 denier, 1%," average length were soaked in the following solutions:

A. 1.2% diethanol sulfone 1% Na CO pH about 10.5

1.2% diethanol sulfone 3 MgCl pH about 7.2

1.2% diethanol sulfone 6% I-ICHO pH about 3.8

1.2% diethanol sulfone 3% MgCl -6H O 6% HCHO pH about 6.4

The solutions were centrifuged to approximately 100% wet pickup, dried for 30 minutes at C. and cured for one minute at 190 C. They were then boiled for 5 minutes in a 1% commercial detergent solution, rinsed and dried. Following this they were analyzed for sulfur.

The sample treated with solution A, which is the standard procedure conventionally used to react diethanol sulfone with cellulose, contained 0.66% S. The sample treated with solution B contained 0.19% S and that treated with solution C, 0.15% S. The sample treated with solution D contained 0.52% S.

After prolonged scouring at pH 8, samples A and D were substantially unchanged while only trace amounts of sulfur remained in samples B and C.

This demonstrates the fact that both a Lewis acid and formaldehyde are essential for binding diethanol sulfone to cellulose at neutral or acid pH.

Example 3 Samples of rayon challis were treated in the following solutions:

1.2% diethanol sulfone 1% Na CO pH 10.5

B. 1.2% diethanol sulfone 3% Zn(NO -6H O 6% HCHO pH 3.4

The samples were padded to wet pickup, framed to dimension, and dried at 80 C. for 10 minutes. After removal from the frame they were cured at C. for 1 /2 minutes and boiled off for 5 minutes in a 1% commercial detergent solution. Part of each sample was steeped in 1 N NaOH for 1 hour at 80 C. and then an analysis for sulfur was made. The results were as This demonstrates the superior resistance to alkali bydrolysis of fabric treated according to the invention, compared with conventionally treated fabric.

7 Example 4 Samples of cotton broadcloth were treated with the following solutions:

3% MgCl -6H O 4% HCHO pH 6.9

The samples were padded, dried, cured and boiled oil as in Example 3. Portions of each sample were steeped in Samples A were treated with an aqueous solution having pH of 10.5 and containing (weight percent) Diethanol sulfone 1.2 Soda ash 1 Borax 0.2

Samples B were treated with a solution having a pH of 3.2 and containing (weight percent) Diethanol sulfone 1.2 HCHO 6 Zn(BF 3 After drying, curing, and soap b-oil oil, as in Example 3, all samples were exposed to actinic radiation in a fadeometer until just appreciable fading was noted. The results were as follows:

1 N NaOH, as in Example 3. The samples Were analyzed Samples: Hours recorded for sulfur and formaldehyde and tested for wet and dry Remazol A crease recovery angle. The results are tabulated below: Remazol B 60 Percent S Percent ORA (W-l-F) HCHO Dry Wet Before After Bound NaOH NaOH Sample treated with Solution A. 0. 97 0.15 217 252 Sample treated with Solution B 0. 54 0.38 0.81 277 280 Control (untreated) 125 159 2 Crease Recovery Angle, degrees, warp and filling. Sample A bad yellowed excessively; sample B but slightly. Paranol A These tests indicate that treatment according to the in- Paranol B vention gives a better balance between wet and dry crease recovery properties than the conventional alkaline catalyst system.

Example 5 Samples of rayon challis were treated according to 2.4% diethanol sulfone 4% MgCI -6H O 6% HCHO In addition to the tests listed in Example 4, samples in the case were tested for grab tensile strength and Elmendorf tear strength. The results are tabulated below:

Thus it is clear that the present technique of applying diethanolsulfone affects the light fastness of representative dyes very much less than the conventional technique.

I claim:

1. A process for improving the properties of cellulose which comprises impregnating cellulose With diethanol sulfone, with formaldehyde and with a metallic salt which is a Lewis acid in the solid state and curing the impregnated cellulose.

2. The process claimed in claim 1 wherein the metallic salt is a magnesium salt.

3. The process claimed in claim 2 wherein the magnesium salt is a magnesium halide.

4. The process claimed in claim 3 wherein the magnesium halide is magnesium chloride.

5. A method for improving the properties of cellulose which comprises impregnating the cellulose with an aqueous solution having a pH between about 1 and about 10 and containing diethanol sulfone, formaldehyde and a metallic salt which is a Lewis acid in the solid state, dry- Percent S Percent ORA (W+F) GT, ET, H CH0 Dry Wet lbs. g. Before After Bound NaOH NaOH Sample treated with Solution A 1. 46 0. 45 226 236 35. 5 866 Sample treated with Solution B 0. 54 0. 39 l. 92 267 249 32. 7 952 Control (not treated) 185 191 71. 0 1, 440

3 Grab Tensile Strength. 4 Elmendorf Tear Strength. Fabrics, D39, p. 4.

Sample A was badly yellowed; sample B only slightly.

Example 6 Samples of cotton broadcloth were dyed, using conventional procedures with 1% Remazol Brilliant Blue R, a fiber reactive dye, and 1% Paranol Fast Blue 4 GL' (Color Index Direct Blue 78; No. 34200). Each sample was split in half. The halves were marked A and B.

See ASTM Standards on Textile Materials, October 1959, Tests for Woven ing the impregnated cellulose and heating the dried material to react the cellulose, formaldehyde and diethanol sulfone.

6. The method claimed in claim 5 wherein at least about 0.003 mol of metallic salt are deposited on the cellulose, per g. of cellulose.

7. The method claimed in claim 5 wherein at least about 0.003 mole of metallic salt and at least about 1 g.

9 of diethanol sulfone, per 100 g. of cellulose, are deposited on the cellulose, together with sufiicient formaldehyde so that after drying, and subsequent reaction, at least about 0.1 g. of formladehyde are bound. to the cellulose, per 100 g. of cellulose.

8. A method for improving the properties of cellulose which comprises impregnating the cellulose with an aqueous solution containing between about 1 and about 10% by weight diethanol sulfone, between about 0.5 and about 10% by weight formaldehyde and between about 0.03 and about 0.9 mol/liter of a metallic salt which is a Lewis acid in the solid state, and heating the impregnated material to dry it and to effect reaction 'between the cellulose, the formaldehyde and the diethanol sulfone.

9. The method claim in claim 8 wherein the pH is between about 1 and about 10.

10. A method for improving the properties of cellulose which comprises impregating cellulose with diethanol sulfone, with formaldehyde and with the salt of a Group II metal and a strong monobasic acid which is at least 50% ionized in normal aqueous solution at- 18 C., and curing the impregnated cellulose.

11. An aqueous solution suitable for treating textile which comprises at least 1% by weight diethanol sulfone, at least 0.5% by weight formaldehyde and at least 0.03 mol/liter of a metallic salt which is a Lewis acid in the solid state.

12. The solution claimed in claim 11 wherein the Lewis acid is a magnesium salt.

13. The solution claimed in claim 12 wherein the magnesium salt is a magnesium halide.

14. The solution claimed in claim 12 wherein the magnesium salt is magnesium chloride.

15. The solution claimed in claim 4 and having a pH between about 1 and about 10.

16. An aqueous solution comprising between about 1 and about 10% by Weight diethanol sulfone, between about 0.5 and about 10% by weight formaldehyde and between about 0.03 and about 0.9 mol/liter of a salt of a Group II metal and a strong monobasic acid which is at least ionized in normal aqueous solution at 18 C.

17. Cellulose cross linked by a reaction product of formaldehyde and diethanol sulfone.

18. Cellulose containing, by weight, at least about 0.1% formaldehyde and about 0.5% diethanol sulfone chemically bound thereto.

19. Cellulosic textile material containing, by weight, between about 0.1 and about 7% formaldehyde and between about 0.5 and about 5% diethanol 'sulfone chemically bound thereto.

References Cited by the Examiner UNITED STATES PATENTS 2,878,294 3/1959 Kress. 2,988,417 6/ 1961 Emmons. 3,113,826 112/1963 Daul et al. 81l6.4

OTHER REFERENCES Welch et al., Textile Research Journal, vol. 31, pp. 8486 (1961).

J. TRAVIS BROWN, Acting Primary Examiner.

NORMAN G. TORCHIN, Examiner.

J. CANNON, Assistant Examiner. 

1. A PROCESS FOR IMPROVING THE PROPERTIES OF CELLULOSE WHICH COMPRISES IMPREGNATING CELLULOSE WITH DIETHANOL SULFONE, WITH FORMALDEHYDE AND WITH A METALLIC SALT WHICH IS A LEWIS ACID IN THE SOLID STATE AND CURING THE IMPREGNATED CELLULOSE. 